Q.Find out various applications or use of gold nanoparticles.

At the nanoscale, different physical laws dominate a material's behaviour compared with everyday, human-scale experience, so a substance's bulk properties cannot simply be assumed to hold once it is reduced to nanoscale particles. Colour changes: elemental gold is shining yellow in bulk, but about 100 gold atoms arranged in a cube would appear red -- the same underlying effect that gives ancient gold-nanoparticle-containing glass its historic ruby-red colour. Surface area rises sharply as a bulk material is subdivided into smaller particles (the total volume stays fixed, but the total exposed surface grows, e.g. a 1 m cube's 6 m^2 surface area rises to 18 m^2 once cut into 27 smaller cubes), giving nanoparticles far greater chemical reactivity and making nanoparticle catalysts (Pd/Pt for hydrogenation, TiO2/ZnO for photocatalysis) far more active and easily separated/recycled than bulk equivalents; gold, chemically unreactive in bulk, becomes a good catalyst as nanoparticles. Thermal properties shift t …